One technology for after-treatment of engine exhaust utilizes selective catalytic reduction (SCR) to enable certain chemical reactions to occur between NOx in the exhaust and ammonia (NH). NH3 is introduced into an engine exhaust system upstream of an SCR catalyst by injecting urea into an exhaust pathway. The urea entropically decomposes to NH3 under high temperature conditions. The SCR facilitates the reaction between NH3 and NOx to convert NOx into nitrogen (N2) and water (H2O). However, as recognized by the inventor herein, issues may arise upon injecting urea into the exhaust pathway. In one example, urea may be poorly mixed into the exhaust flow (e.g., a first portion of exhaust flow has a higher concentration of urea than a second portion of exhaust flow) which may lead to poor coating of the SCR and poor reactivity between emissions (e.g., NOx) and the SCR. Additionally, overly mixing and agitating the urea in the exhaust can likewise cause issues, such as increased deposits.
Attempts to address poor mixing include introducing a mixing device downstream of a urea injector and upstream of the SCR such that the exhaust flow may be homogenous. One example approach is shown by Liu et al. in U.S. Pat. No. 8,756,913. Therein, an exhaust gas sensor module is introduced to an exhaust pathway to help increase an exhaust gas homogeneity. The exhaust gas sensor module comprises a plus-shaped (e.g., cross-shaped) tube with a plurality of perforations along a face of the module facing a direction opposite exhaust flow. The exhaust gas enters the module and flows to a gas sensor and then exits the module via a single conical opening. There may be a second module, identical to the first module described above, located downstream of the first module with an exhaust component located between the first module and the second module.
However, the inventors have also recognized potential issues with such systems. As one example, by introducing two identical modules in an exhaust stream, the mixing in both the modules is also identical. In this way, an alteration in exhaust gas direction is reduced and thus, the randomness of the mixing may be reduced. Furthermore, a sensor is located inside each of the modules. Thus, the sensor is limited to measure only portions of the exhaust gas the module is capable of intercepting in the exhaust conduit.
In one example, the issues described above may be addressed by a mixer comprising a pair of cylindrical tubes perpendicularly intersecting along a central axis of an exhaust conduit, where each of the cylindrical tubes comprise two oblong inlets proximal to an exhaust conduit wall and two angled circular outlets proximal to the central axis facing toward, away from, and perpendicular to a direction of exhaust flow. In this way, exhaust gas flowing out of the mixer flows to regions of the exhaust conduit unperturbed by the mixer and increases an overall homogeneity of exhaust gas in the exhaust conduit. Thus, mixing is increased and a composition of exhaust gas throughout the entire exhaust conduit is substantially equal.
As one example, the mixer may intercept exhaust gas along an outer periphery of the exhaust conduit and allow the exhaust gas to collide and mix at a region of confluence located along a central axis of the mixer. The mixed exhaust gas flows into the exhaust conduit to be further mixed with unmixed exhaust gas of the exhaust conduit by flowing parallel to or perpendicular to an unmixed exhaust gas flow.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.